1. Field of the Invention
The present invention relates to an internal combustion engine with a supercharger.
2. Description of the Related Art
Conventional supercharged internal combustion engines are usually provided with superchargers, having a compression ratio smaller than that of engines of a natural intake type (NA engines). For example, a Honda "City Turbo II" engine described in a magazine "Motor Fans", page 117, January, 1984, has a specification as follows:
(1) Type of Engine: Water-cooling, in-line 4-cylinder PA1 (2) Displacement: 1,231 cc PA1 (3) Bore size of cylinder: 66 mm PA1 (4) Stroke of piston: 90 mm PA1 (5) Compression ratio (.epsilon.): 7.6 PA1 (6) Supercharger: Turbocharger (charging pressure, 0.85 kg per cm.sup.2) PA1 (1) Bore size of cylinder: from approximately 43 mm to 67 mm; PA1 (2) Volume of single chamber: from approximately 110 cc to 400 cc; and PA1 (3) S/B ratio: &gt;1. PA1 N is the speed of rotation of the engine represented in rpm; and PA1 S is the stroke of the piston as represented in millimeter. PA1 .eta..sub.v is the efficiency in volume as represented in %; PA1 a is the sonic speed as represented in cm per second; PA1 .theta. is the angle of a crank as represented in deg. CA. ATDC; PA1 .theta..sub.IC is the timing for closing the intake valve; PA1 .theta..sub.IO is the timing for opening the intake valve; PA1 N is the speed of rotation of the engine as represented in rpm; PA1 Fi is the area of the opening of the intake valve as represented in cm.sup.2 ; and PA1 Fim(e) is the mean area of the opening of the intake valve as represented in cm.sup.2. PA1 Fia(e) is the effective angular area of the intake valve. PA1 (a) the two intake valves have the same valve sizes; PA1 (b) the two exhaust valves have the same valve sizes; PA1 (c) a ratio of an area of the intake valve to an area of the exhaust valve at their throat portions is 1.5 to 1; and PA1 (d) the efficiency in volume (.eta..sub.v) is set to 100%. PA1 (1) the distance between the valve seat of the first intake valve and the valve seat of the second intake valve is 2.5 mm or over; PA1 (2) the distance between the valve seat of the intake valve and the valve seat of the exhaust valve is 3.5 mm or over; PA1 (3) the distance between the valve seat of the first exhaust valve and the valve seat of the second exhaust valve is 4.0 mm or over; PA1 (4) the distance between the valve seat of the intake valve and an ignition plug is 2.5 mm or over; PA1 (5) the distance between the valve seat of the exhaust valve and the ignition plug is 3.5 mm or over; PA1 (6) the valve seat may come into contact with a peripheral portion of the bore of the cylinder; PA1 (7) the angle between the valves is 30.degree.; PA1 (8) the combustion chamber is of a penthouse type; PA1 (9) the diameter of the plug is 14 mm; PA1 (10) the diameter of a stem is 6 mm; PA1 (11) the diameter of the throat portion=the diameter of the valve seat minus 5 mm; PA1 (12) the length of a valve lift is 8.5 mm; and PA1 (13) the timing for opening the valve is 256 deg CA. PA1 (1) If the speed of rotation of the engine N.sub.0.5 is larger than the speed of rotation of the engine N.sub.20, the bore size is set so as to allow a sufficient amount of the intake air to enter up to a speed higher than the limit upon reliability as described hereinabove. Hence, this is to the contrary of the original purpose that the bore size should be made smaller, so that the speed of rotation of the engine N.sub.0.5 should be equal to or smaller than the speed of rotation of the engine N.sub.20. PA1 (2) It can be noted that the speed of rotation of the engine that produces the maximum horse power is generally set to the speed of rotation of the engine lower by approximately 1,000 rpm than the limit upon reliability. PA1 (3) When the characteristics of the engine are to be set in the same manner as conventional engines, it is preferred that the speed of rotation of the engine that produces the maximum horse power should be set to larger than 6,000 rpm. Hence, the speed of rotation of the engine N.sub.0.5 should be set to larger than 6,000 rpm. PA1 (4) In order to ensure the predetermined volume in the single chamber and to minimize the bore size, it is necessary to place a limit upon the stroke of the piston; however, even if the bore size would be minimized, it is not necessary to shorten the stroke of the piston to such an extent to which a limit is placed upon the speed of rotation of the engine so as to exceed by far the speed of rotation of the engine of the conventional engine. Hence, the speed of rotation of the engine N.sub.20 should be set to 8,000 rpm or slower.
Further, a Honda "City Turbo II-R" engine, i.e. a racing engine of the City Turbo II engine, has a charging pressure increased to 1.63 kg per cm.sup.2, although its compression ratio is not known.
Internal combustion engines with superchargers are adapted to forcibly fill their cylinders with a mixed fuel so that they have the tendency that the temperature of exhaust gases becomes higher than that of exhaust gases from the NA engines. As the magnitude of the charging pressure becomes higher, the extent to which the temperature of the exhaust gases elevates becomes larger, and there is the risk that reliability upon an exhaust system may be impaired due to exhaust gases having high temperature, particularly at the time when the engine is running with a full open load. It can be noted herein that the "City Turbo II-R" engine is so designed as to be run for two to three hours, not for a long period of time, with a full open load, so that no problem with reliability upon the exhaust system may arise even if the temperature of the exhaust gases would be high.